The present invention relates to a safety device of an industrial robot for-assuring safety of operator teaching closely to a robot main body.
Generally, in the industrial robot of teaching playback system, in order to teach the robot, a teaching pendant (TP) is used as a portable console. This teaching pendant is useful for teaching while moving the robot finely by directly observing a control point (end effector) of the industrial robot by the teaching operator, and most teaching pendants are designed to be held by one hand and operate for teaching by other hand.
This teaching pendant is provided with a dead-man's switch for assuring safety of the teaching operator. Only while the teaching operator is pressing this dead-man's switch, the servo power source is supplied and teaching operation is enabled. When the teaching operator releases this dead-man's switch, the servo power source for driving the servo motor is cut off, and the shaft of the servo motor is braked at the same time, and the robot stops immediately, so that the safety of the teaching operator is protected.
The robot main body is limited in a range of motion by the software, and an over-travel switch is provided outside of the motion range by the software. In case, due to some abnormality, the robot moves out of the range, the over-travel switch is opened to cut off the servo power source for driving the servo motor, and the servo motor is braked to stop the robot immediately, so that dangerous runaway can be prevented.
Moreover, according to a safety circuit, by the input from a door switch which opens the circuit when the door of safety fence is opened, an emergency stop push-button switch provided in the teaching pendant, or an emergency stop push-button switch provided in the operation panel or outside, the servo power source for driving the servo motor is cut off, and the servo motor is braked, thereby bringing the robot into an emergency stop.
A conventional safety switch of industrial robot is described below while referring to FIG. 3.
In FIG. 3, when a teaching pendant enable switch 10 is closed, the servo power source can be turned on at the teaching pendant side. That is, if there is no other disturbing factor, the servo power source can be turned on by pressing a dead-man's switch 101 of the teaching pendant.
When the teaching pendant enable switch 10 is closed, the central processing unit (CPU) sets a teach disable signal 19 in low logic, and a relay coil CR1 is not energized. That is, a contact CR1a is open, and a contact CR1b is closed, and a signal line 101a connected to the dead-mPn's switch 101 provided in a teaching pendant 4 is connected to a grounding line PG through the contact of the dead-man's switch 101 and relay contact CR1b. Since the signal line 101a is connected to the CPU through a photo coupler, when there is a conduction between the signal line 101a and grounding line PG, the CPU recognizes that the dead-man's switch 101 is closed.
When the dead-man's switch 101 is closed in the closed state of the teaching pendant enable switch 10 of the teaching pendant 4, the CPU sets the servo power source ON signal 13 to high logic, and a relay coil CR13 is energized, and its contact CR13a is closed. On the other hand, when the dead-man's switch 101 is closed, a relay coil CR2 is energized, and its contact CR2a is closed. Therefore, as far as there is no impeding factor for turning on the servo power source (for example, in the case of the apparatus in FIG. 3, when an over-travel switch 105 is open, a door switch input 106 of safety fence is open, an external emergency stop input 107 is open, or an emergency stop input 104 of the teaching pendant 4 is open), all of the relay contacts CR18a, CR14a, CR17a, CR16a, CR13a, and CR2a are closed, and a voltage (+DC 24 V in the example in FIG. 3) is applied to the line of a servo power source ON enable signal 12, so that the servo power source can be turned on.
In a robot main body 1, moreover, the moving range is limited usually by the software, and the over-travel switch 105 is provided outside of the moving range by this software, and if the robot gets out of this range due to some abnormality, the over-travel switch 105 is opened. As the over-travel switch 105 is opened, the signal line 105a is cut off from the grounding line PG. Since the signal line 105a is connected to the CPU through the photo coupler, as the signal line 105a is cut off from the grounding line PG, the CPU recognizes that the over-travel switch 105 is opened, and sets the servo power source ON signal 13 to low logic, and hence the relay coil CR13 is de-energized, thereby opening its contact CR13a, and the line of the servo power source ON enble signal 12 has no voltage and the servo power source is cut off. As the servo power source is cut off, it is designed so that the servo motor is braked, and thereby the robot is brought into an emergency stop, so that -dangerous runaway of the robot can be avoided.
The door switch input 106, emergency stop input 104 of teaching pendant 4, external emergency stop input 107, and panel emergency stop input 108 are normally closed contact signals with no voltage, and the relay coils CR16, CR14, CR17, and CR18 are energized. These relay contacts CR16a, CR14a, CR17a, and CR18a are connected in series, and are further connected to the line of the servo power source ON enable signal 12 through the relay contacts CR13a and CR2a . When the external contact of the normally closed circuit of any one of the door switch input 106, emergency stop input 104 of the teaching pendant 4, external emergency stop input 107, and panel emergency stop input 108 is opened, one of the relay coils CR16, CR14, CR17 and CR18 is deenergized, and any one of the relay contacts CR16a, CR14a, CR17a, and CR18a is opened, and the line of the servo power source ON enable signal 12 has no voltage, and the servo power source is cut off. When the servo power source is cut off, it is designed so that the servo motor is braked, and the robot is stopped immediately, and danger is avoided.
Thus, the safety device of the industrial robot is composed of micro switch contacts as dead-man's switch and over-travel switch and relay contacts. Depending on opening and closing of the micro switch contacts and relay contacts, the servo power source of the industrial robot is turned on or cut off. In the conventional safety device of industrial robot, however, since the servo power source is controlled by using a single contact, if fusion occurs in the contacts, emergency stop signals of dead-man's switch, overtravel switch and others are not normally transmitted, and specified function cannot be executed, and safety cannot be assured, which was a fatal defect.